Yet the place most people touch computers is on the desktop. Everyone expects that they will have the tools available that currently are shipped with Windows. There are two basic issues.
The first issue is making tools which are compatible with the Windows programs. That is, tools which will read and write Microsoft file formats. XML is an attempt to standardize the file formats so information is not locked up in things like .doc files. Microsoft, in order to fight this threat, is patenting its Windows file formats.
The second issue is making Linux accessible to the average user. It is claimed that Linux is hard to install. Windows installations are just as hard but they are done by the manufacturer. Dell and others have started campaigns to sell pre-installed Linux systems but Microsoft has threatened their business (by refusing to license Windows) and the manufacturers have all withdrawn from their attempts. As you can see from this class the KNOPPIX distribution makes installations nearly painless.